“further” vs. “farther”

Is there a difference between “further” and “farther”? David Attenborough (age 86, I think) says “farther”. I have never, ever, used that word. What’s the difference, if there is one? My dictionary does not say they are synonyms, but their definitions are identical. “Nothing could be farther from my mind” sounds to me a bit over the top, like saying ‘looking glass’ when you mean ‘mirror’. Views?

In the past they were more or less interchangeable, until the end of the 19th century an editor of the OED thought the distinction would be useful. In Britain, Fowler strongly disagreed with him, and his advice was more or less ignored. But in North America his idea was taken up and some (but by no means all) people now insist on the distinction that Dai Alanye makes.

On one thing we're all agreed - farther is only use for distance, not 'more' or 'in addition to'. But in Britain we have no restrictions ion the use of further to the meaning of 'more'.

In Britain, as Fowler predicted would happen, most people use further for everything, a process that started in the first half of the 19th century:

So, as farther is not used very much, it could sound a bit old-fashioned to some younger generations.

A site search of the BBC brings up 19,400 for further, 134 for farther. The ratios further to farther are 307,000 to 11,400 at the Guardian, 257,000 to 2,200 at the Independent and 182,000 to 4590 at the Telegraph.

Most of the stuff on the Internet gives the American angle, with the distinction, so last year I wrote a post giving the British perspective:

@bubbha - and a lot of American commentators will swear blind that this is set in stone, so if writing for an American audience, it's perhaps better to stick to it. But this is rather an artificial rule and a relatively new distinction (see my comment above). In Britain we've more or less eliminated the problem by using further for everything - farther is pretty rare nowadays in British English.

I'm in NZ and I hardly every use (or hear) "farther"; it has largely fallen out of use I think.The only time I'd really want to use "farther" and the superlative "farthest" is if I was talking about distances measurable in light years: "the farthest galaxies". Somehow in that situation plain old "further"/"furthest" doesn't cut it any more.